Terpyridine-Containing Porphyrin and Coordination Assembly with Fullerene-Based Pyridine for Enhanced Electrocatalytic Oxygen Evolution and Photocurrent Response

A novel terpyridine-modified porphyrin, ZnP-Pr-tpy, has been synthesized and characterized successfully using elemental analysis, mass spectrometry (MS), nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR) and ultraviolet/visible spectroscopy (UV-Vis). Studies by steady-state fluorescence and UV-visible spectroscopies show that a supramolecular dyad is formed by fullerene-based pyridine (C-60-py) and the zinc porphyrin via a coordination bond, with a binding constant K of 1.18 x 10(5) M-1. The photoexcitation of ZnP-Pr-tpy causes the ground state electrons of the tpy moiety to shift to the ZnP unit via an electron-exchange process following the Dexter energy transfer mechanism. Thus, a donor-acceptor composite film, ZnP-Pr-tpy/C-60-py, was fabricated by combining the photosensitizer ZnP-Pr-tpy with C-60-py. A comparison of the over-potential at 10 mA/cm(2), the Tafel slopes and the photocurrent response under visible light irradiation showed the electrocatalytic oxygen evolution reaction (OER) and the photocurrent response to be clearly improved by the covalent modification of the porphyrin with terpyridine, and further improved by the axial coordination of C-60-py to ZnP-Pr-tpy. These improvements are attributed to increased intra- and intermolecular electron transfer, the decrease in the electrochemical impedance resulting from the axial coordination of C-60-py to ZnP-Pr-tpy and the electron-exchange in ZnP-Pr-tpy through the Dexter energy transfer mechanism under light excitation. (C) 2020 Elsevier Ltd. All rights reserved.